Thursday, July 12, 2007

Mice Get "Human" Vision in Gene Experiment

A mouse drinks a drop of soy milk as a reward for correctly identifying which of three illuminated panels is a different color from the other two.
The rodent was part of a genetic experiment that gave it enhanced color vision much like that of humans. Normally mice see only blues, grays, and yellows.
Photograph by Gerald Jacobs, courtesy Howard Hughes Medical Institute

Mice Get "Human" Vision in Gene Experiment
Anne Minard
for National Geographic News
March 22, 2007

Give a mouse the right new genes, and presto—it'll see like people do.

Researchers have added genes to the genomes of lab mice that are "blueprints" for a class of color receptors unique to primates, such as humans, apes, and monkeys.

With their new genes, some of the mice passed tests showing they were able to see in "full color," trichromatic vision. Normally mice see a muted array of grays, blues, and yellows.

The findings hint that mammal brains (including our own) are extremely adaptable—ready to process inputs they didn't even know existed.

The study also raises the possibility that color vision as we know it could have arisen from a single mutation.

(Related: "New Mouse Teeth, Whiskers Grown From Handful of Cells" [February 26, 2007].)

New Visual Realm

Trichromacy depends on three types of photoreceptor cells in the eye, which absorb light at different wavelengths.

For example, short-wavelength receptors are most sensitive to blues, medium-wavelength receptors are most sensitive to greens, and long-wavelength receptors are most sensitive to reds.

When light hits the receptors, the brain compares their responses to perceive color.

Normally, nonprimate mammals see with dichromatic color vision, because their brains contain receptors only for short and medium wavelengths. This makes most mammals somewhat color-blind, relative to primates.

The new study is by Gerald Jacobs of the University of California, Santa Barbara, and colleagues at Johns Hopkins School of Medicine and Howard Hughes Medical Institute, both in Baltimore, Maryland. The findings will be published in tomorrow's issue of the journal Science.

The new, long-wavelength receptors immediately opened up a new visual realm to mice, the researchers say.

The study results also show that mammals' nervous systems are remarkably adaptable.

"We think this has implications not just for the evolution of visual systems but for sensory systems in general," Jacobs added.

In other words, animals' brains may be primed to process new sights, smells, tastes, or sounds just as soon as their bodies evolve the abilities to detect "new" phenomena.

Quite Surprising

Daniel Osorio is a neuroscientist at the University of Sussex in Britain.

He said the discovery that simply giving mice a new type of photoreceptor allows full-color vision "is quite surprising."

"This ability allows mice to cope with new types of visual environment and hence contributes to their adaptability as a species," Osorio said.

He added that the study debunks a common explanation about why only primates are able to see in trichromatic vision: because they're the only ones with the brains to handle it.

"It is evident," he said, "that mice could do what primates did."

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